COMBINED EFFECTS OF GIBBERELLIN AND 2,4-D ON DORMANT SEEDS OF STINKWEED (THLASPI ARVENSE L.)

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Abstract
Concentrations of 50 and 500 p.p.m. gibberellin were used alone and in combination with 2,4-D sodium salt solutions ranging from 0.00001 to 8000 p.p.m. acid equivalent, in Petri dishes, with dormant seeds of stinkweed (Thlaspi arvense L.), to determine the effects of these treatments or of subtoxic amounts of 2,4-D alone, on germination and growth. About 90% germination within 2 weeks was induced by the 50 p.p.m. gibberellin and was not augmented by the very dilute concentrations of 2,4-D. Complete germination occurred within only 8 days with 500 p.p.m. gibberellin alone. Strengths greater than approximately 0.02 p.p.m. of 2,4-D retarded shoot elongation and concentrations greater than about 0.5 p.p.m. of 2,4-D progressively reduced germination associated with either 50 or 500 p.p.m. gibberellin. Concentrations of 2,4-D higher than approximately 200 p.p.m. prevented both concentrations of gibberellin from causing any true germination. Beyond 200 p.p.m. of 2,4-D there was still, however, a broad range within which gibberellin was able to cause a definite initial phase of the germination process characterized simply by rupture of the seed coat without protrusion of root and stem. This response could not be prevented by 2,4-D at concentrations lower than 4000 p.p.m. in counteraction with 50 p.p.m. gibberellin, or at dosage lower than about 7000 p.p.m. in association with 500 p.p.m. gibberellin. Potential practical significance of the work is considered.